WASHINGTON — The three companies bidding to succeed the retired space shuttle as NASA’s means of sending astronauts to and from the international space station have different fallback plans for their respective vehicles should they get passed over for a final round of government development funding, the award of which is imminent.

Representatives of these companies — Boeing Space Exploration of Houston; Sierra Nevada Corp. (SNC) Space Systems of Louisville, Colorado; and Space Exploration Technologies Corp. of Hawthorne, California — offered their perspectives during an Aug. 5 panel discussion in San Diego at the American Institute of Aeronautics and Astronautics’ Space 2014 conference.

NASA’s fourth major commercial crew funding award, the fixed-price Commercial Crew Integrated Capability (CCtCap) contract, will provide at least one of these three companies with financial assistance to complete development and safety certification of its proposed transportation system, plus a fee for the first crewed U.S. space launch since the shuttle retired in 2011. That round trip to the space station is notionally scheduled for late 2017.

Boeing, which is offering a capsule called CST-100 that would be launched by a United Launch Alliance Atlas 5 rocket, sees little reason to continue developing the craft without a helping hand from NASA, John Mulholland, vice president and general manager of commercial programs, told the audience.

Mulholland said closing the business case for CST-100 without NASA as an investor and anchor customer “would be very difficult to do.”

SpaceX, by contrast, will continue developing a crewed version of its Dragon logistics capsule regardless of whether it wins a CCtCap award, said Garrett Reisman, former astronaut and Dragon Rider program manager.

“We certainly hope we can proceed in partnership with NASA,” Reisman said. But “we’re not going to stop.”

The former shuttle crewman did concede that a lack of NASA investment would “change things dramatically” for SpaceX, slowing development of the company’s human-rated systems.

SNC Space Systems Corporate Vice President Mark Sirangelo said his company, which distinguished itself from the pack by proposing a lifting-body vehicle called Dream Chaser that resembles a miniature space shuttle, might press on with the Dream Chaser project even if NASA decides it is not interested in the vehicle.

Sirangelo has pushed hard to keep Dream Chaser, which received the smallest of share of the third round of commercial crew program funding, at the forefront of the conversation. The Dream Chaser program has attracted a transcontinental network of international partners, including the German and Japanese space agencies.

These developments have led Sirangelo to suggest that Dream Chaser, which would also launch on an Atlas 5, could find a market besides servicing the space station for NASA.

“I think we are now in a place where it is possible to continue,” Sirangelo said. “I’m not saying we can or we can’t — that’s something we’d have to discuss.”

Weeks after the panel discussion in San Diego, NASA declined to address rumors swirling around Washington that the CCtCap winner, or winners, would be announced during the final week of August.

“We don’t have a scheduled date for the award(s),” NASA spokeswoman Stephanie Schierholz said via email Aug. 22. “NASA will make the award(s) sometime in August or September.”

Meanwhile, the three companies are in the late stages of work NASA helped pay for with some $1.1 billion worth of Space Act Agreements awarded in 2012.

Boeing is set to wrap up its share of this work in August, according to a copy of its roughly $460 million Space Act Agreement. SpaceX and Sierra Nevada, which received $440 million and $212.5 million, respectively, in third-round funding, have until March 31 to wrap up their work.

During an Aug. 7 meeting at NASA headquarters here, Kathy Lueders, the agency’s commercial crew program manager, told the NASA-chartered Aerospace Safety Advisory Panel the agency wants to keep working with all three commercial crew hopefuls, whether or not they receive CCtCap contracts.

There is a precedent for such an arrangement.

After the second round of commercial crew funding, NASA signed an unfunded Space Act Agreement with the secretive Blue Origin rocket company established by Amazon.com founder Jeff Bezos. The agreement gave Blue Origin of Kent, Washington, access to NASA facilities and expertise.

The commercial crew program is not the only potential source of NASA funding for the aspiring providers. On Sept. 30, NASA will release a solicitation for cargo delivery service to station between 2017 and 2024. The commercial crew hopefuls have all indicated they are interested in bidding, and possibly taking cargo work away from incumbents SpaceX and Orbital Sciences Corp. of Dulles, Virginia.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.